Rechargeable batteries suffer from a "memory effect", which limits the life of a rechargeable battery. The "memory effect" is caused by the incomplete discharging of a battery before the battery is recharged. The continual failure to completely discharge a battery before the battery is recharged creates a "memory effect", where the battery "remembers" the level to which it was discharged. In subsequent use, the battery will discharge to the level that it "remembers" discharging to (instead of completely discharging), which reduces the useful life of the battery between charges.
Although it is recognized that older types of nickel-cadmium (NiCad) batteries are subject to a "memory effect", battery manufacturers claim that newer types of NiCad batteries, nickel metal hydride (NiMH) and Lithium batteries (lithium ion (Li-ion) or lithium-polymer batteries) are not subject to the "memory effect". For example, in the owner's manual for the SONY.TM. Digital Still Camera MVC-FD83/FD88 it states "You may also charge a partially used pack whenever you desire with no adverse affect on the battery pack."
In EDN Access Magazine in the cover story of the Feb. 4, 1999 edition entitled "Batteries Clean Up Their Act" by Dan Strassberg it is stated that "Most battery manufacturers insist that memory effect is an urban legend. . ." The article goes on to state,
"Whereas battery manufacturers generally agree that the memory effect is fiction, most concede that you might confuse a real phenomenon called `voltage depression` with memory effect. However, according to legend, the memory effect is irreversible, whereas voltage depression is fully reversible."
The invention recognizes that even the newer NiCad batteries NIMH batteries and Lithium batteries are subject to the memory effect or voltage depression.
It would be advantageous to extend the lifetime of a battery